I'd try to stick with novice matches as best you're able. They force you to use some viable options. The Pyra is a bit easier, since you just have to blow them up, and the weapon loadout makes that pretty easy. You can still do it with the goldfish, but that requires a little more finesse on the pilot's part. Pivoting the ship to shoot the side guns at times. You can always use kerosene and get very rammy with these ships as well.
On a carronade goldfish, you generally want to stay out of their gun arcs and just take out their balloon repeatedly. It's not that hard to maneuver into their blind spot as they're sinking, but you have to be careful when following them down (the carronade doesn't aim down very well). Usually as they near the ground I switch to a flamethrower or something explosive, since those guns have a large turning radius. You can easily stay above them while doing damage, often keeping them pinned there with the flamer.
A hwacha goldfish is pretty popular, but takes a bit more planning. You can't afford to miss shots, since that reload is so long. Fire a barrage and disable their ship up close (or mid range if you have a good gunner) and attempt to get into their blind spot, using your side guns while the hwacha is reloading. The gat is especially useful for taking out their armor. Once the armor goes down, turn back to the now reloaded hwacha and finish them.
If you don't feel like playing in novice matches, I'd still recommend a pyra or goldfish ships. They're by far the easiest for players to get used to. Communication goes a long way as well.
Squid is tricky with it's speed and general fragility; galleon is massive and hard to control (and a very easy target) and harder to organize your crew; junker is another easy-ish ship, but with the guns on the sides of the ship, your gunners have to compensate for your ship movement as well, and can be difficult to hit targets for newer gunners; spire is a great gun ship, but also really fragile and difficult to control; and finally the mobula is another great gun ship, but you have massive blindspots and need the most crew coordination.